U.S. patent number 10,934,198 [Application Number 16/873,135] was granted by the patent office on 2021-03-02 for relative non-wettability of a purification membrane.
The grantee listed for this patent is Mansour S. Bader. Invention is credited to Mansour S. Bader.
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United States Patent |
10,934,198 |
Bader |
March 2, 2021 |
Relative non-wettability of a purification membrane
Abstract
Methods are herein provided for preparing a material for casting
a flat-sheet, extruding a solid-fiber, and/or extruding a
hollow-fiber utilizing a chlorinated aqueous amine solution as an
effective solvent to form a crystalline polymorph structure of the
material. This material in the form of, for example, an effective
vapor permeable membrane can be used in membrane distillation to
desalinate saline streams.
Inventors: |
Bader; Mansour S. (College
Station, TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
Bader; Mansour S. |
College Station |
TX |
US |
|
|
Family
ID: |
1000004656622 |
Appl.
No.: |
16/873,135 |
Filed: |
February 8, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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16501510 |
Apr 20, 2019 |
10577269 |
|
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15731999 |
Sep 7, 2017 |
10322952 |
|
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15731626 |
Jul 10, 2017 |
10336638 |
|
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13999309 |
Feb 8, 2014 |
9701558 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C02F
1/004 (20130101); C02F 9/00 (20130101); C02F
1/442 (20130101); C02F 1/72 (20130101); C02F
1/54 (20130101); C02F 1/5236 (20130101); C02F
1/441 (20130101); C02F 2303/22 (20130101); C02F
1/20 (20130101); C02F 2103/18 (20130101); B01D
15/00 (20130101); C02F 2303/20 (20130101); C02F
1/444 (20130101) |
Current International
Class: |
B01D
15/00 (20060101); C02F 9/00 (20060101); C02F
1/00 (20060101); C02F 1/20 (20060101); C02F
1/52 (20060101); C02F 1/54 (20060101); C02F
1/44 (20060101); C02F 1/72 (20060101) |
Field of
Search: |
;210/638 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
US. Appl. No. 16/501,510, filed Apr. 16, 2019, Bader. cited by
applicant .
U.S. Appl. No. 16/501,595, filed May 6, 2019, Bader. cited by
applicant .
Bader, M.S.; Precipitation and Separation of Chloride and Sulfate
Ions from Aqueous Solutions: Basic Experimental Performance and
Modeling; Environ. Progr., 1998, 17, 126-135. cited by applicant
.
Bader, M.S.; Thermodynamics of Ions Precipitation in Mixed-Solvent
Mixtures; J. Hazard. Mater., 1999, B69, 319-334. cited by applicant
.
Ferry, D.; Ultrafilter membranes and ultrafiltration; Chemical
Reviews, 1936, 8, 373-455. cited by applicant .
Hsu, C.C. and Prausnitz, J.M.; Thermodynamics of Polymer
Compatibility in Ternary Systems; Macromolecules; 1974, 7, 320-324.
cited by applicant .
Madorsky, S.L.; Fluorocarbon and chiorocarbon polymers, in: Thermal
degradation of organic polymers, John Wiley & Sons Inc., 1964,
pp. 130-172. cited by applicant.
|
Primary Examiner: Bhat; Nina
Parent Case Text
RELATED APPLICATIONS
This application is a continuation-in-part of my allowed patent
application Ser. No. 16/501,510 filed on Apr. 16, 2019; which is a
continuation-in-part of my patent application Ser. No. 15/731,999
filed on Sep. 7, 2017, now U.S. Pat. No. 10,322,952; which is a
continuation-in-part of my patent application Ser. No. 15/731,626
filed on Jul. 10, 2017, now U.S. Pat. No. 10,336,638; which is a
continuation-in-part of my patent application Ser. No. 13/999,309
filed on Feb. 8, 2014, now U.S. Pat. No. 9,701,558.
This application is also related to my allowed patent application
Ser. No. 16/501,595 filed on May 6, 2019; which is a
continuation-in-part of my patent application Ser. No. 14/998,774
filed on Feb. 13, 2016, now U.S. Pat. No. 10,280,103; which is a
continuation-in-part of my patent application Ser. No. 14/544,436
filed on Jan. 6, 2015, now U.S. Pat. No. 10,259,735; which is a
continuation-in-part of my patent application Ser. No. 14/544,317
filed on Dec. 22, 2014, now U.S. Pat. No. 10,259,734; which is a
continuation-in-part of my patent application Ser. No. 13/066,841
filed on Apr. 26, 2011, now U.S. Pat. No. 8,915,301.
Claims
What is claimed is:
1. A method of preparing a purification membrane by casting a
flat-sheet, said method comprising the steps of: (a) dissolving an
amount of a polymer in an amount of a primary solvent to form a
first solution; (b) mixing an amount of an amine solvent, an amount
of water, and an amount of a chlorine source to form a chlorinated
aqueous amine solution; (c) mixing an amount of said first solution
with an amount of said chlorinated aqueous amine solution to form a
second solution; thereby inducing selective fine crystal clusters
of said polymer, without rapidly precipitating said polymer, and
without degrading the bulk of the structure of said polymer; (d)
casting an amount of said second solution on a substrate; and (e)
phase inverting said substrate in a bath containing only water to
form said flat-sheet.
2. The method of claim 1, wherein said polymer is selected from the
group consisting of polyvinylidene fluoride, polytrifluoroethylene,
polychlorotrifluoroethylene, fluorinated ethylene propylene,
polyhexafluoropropylene, and combinations thereof.
3. The method of claim 1, wherein said primary solvent is selected
from the group consisting of N-methyl-2-pyrrolidone,
N,N-dimethylacetamide, N,N-dimethylformamide, dimethylsulfoxide,
hexamethyl phosphoramide, tetramethylurea, triethyl phosphate,
trimethyl phosphate, acetone, methyl ethyl ketone, tetrahydrofuran,
and combinations thereof.
4. The method of claim 1, wherein said amine solvent is selected
from the group consisting of methylamine, ethylamine,
isopropylamine, propylamine, dimethylamine, diethylamine,
diisopropylamine, dipropylamine, trimethylamine, triethylamine,
tripropylamine, and combinations thereof.
5. The method of claim 1, wherein said chlorine source is selected
from the group consisting of chlorine gas, hypochlorite, and
combinations thereof.
6. A method of preparing a purification membrane by extruding a
solid-sheet, said method comprising the steps of: (a) dissolving an
amount of a polymer in an amount of a primary solvent to form a
first solution; (b) mixing an amount of an amine solvent, an amount
of water, and an amount of a chlorine source to form a chlorinated
aqueous amine solution; (c) mixing an amount of said first solution
with an amount of said chlorinated aqueous amine solution to form a
second solution; thereby inducing selective fine crystal clusters
of said polymer, without rapidly precipitating said polymer, and
without degrading the bulk of the structure of said polymer; (d)
extruding an amount of said second solution through a spinneret to
produce an extruded solid fiber; and (e) phase inverting said
extruded solid fiber in at least a bath containing only water to
form said solid-sheet.
7. The method of claim 6, further comprising replacing the steps
(c) through (e) by the following steps: extruding an amount of said
first solution through said spinneret to produce said extruded
fiber; subjecting said extruded fiber to a bath containing an
amount of said chlorinated aqueous amine solution; and thereafter
phase inverting said extruded solid fiber in said bath containing
said only water to form said solid-sheet.
8. The method of claim 6, wherein said polymer is selected from the
group consisting of polyvinylidene fluoride, polytrifluoroethylene,
polychlorotrifluoroethylene, fluorinated ethylene propylene,
polyhexafluoropropylene, and combinations thereof.
9. The method of claim 6, wherein said primary solvent is selected
from the group consisting of N-methyl-2-pyrrolidone,
N,N-dimethylacetamide, N,N-dimethylformamide, dimethylsulfoxide,
hexamethyl phosphoramide, tetramethylurea, triethyl phosphate,
trimethyl phosphate, acetone, methyl ethyl ketone, tetrahydrofuran,
and combinations thereof.
10. The method of claim 6, wherein said amine solvent is selected
from the group consisting of methylamine, ethylamine,
isopropylamine, propylamine, dimethylamine, diethylamine,
diisopropylamine, dipropylamine, trimethylamine, triethylamine,
tripropylamine, and combinations thereof.
11. The method of claim 6, wherein said chlorine source is selected
from the group consisting of chlorine gas, hypochlorite, and
combinations thereof.
12. A method of preparing a purification membrane by extruding a
hollow fiber, said method comprising the steps of: (a) dissolving
an amount of a polymer in a first amount of a primary solvent to
form a first solution; (b) mixing an amount of an amine solvent, an
amount of water, and an amount of a chlorine source to form a
chlorinated aqueous amine solution; (c) mixing an amount of said
first solution with a first amount of said chlorinated aqueous
amine solution to form a second solution; thereby controlling the
morphology of the outer surface of said hollow fiber; (d) mixing a
second amount of said primary solvent with a second amount of said
chlorinated aqueous amine solution to form a bore liquid; thereby
controlling the morphology of the inner surface of said hollow
fiber; (e) extruding an amount of said second solution and an
amount of said bore liquid through a spinneret to produce an
extruded hollow-fiber; and (f) phase inverting said extruded
hollow-fiber in at least a bath containing only water to form said
hallow-fiber.
13. The method of claim 12, further comprising replacing step (d)
by: mixing said second amount of said primary solvent with an
amount of water to form said bore liquid.
14. The method of claim 12, further comprising replacing steps (c),
(e) and (f) by the following steps: extruding an amount of said
first solution and an amount of said bore liquid through said
spinneret to produce said extruded hollow-fiber; subjecting said
extruded hollow-fiber to a bath containing an amount of said
chlorinated aqueous amine solution; and thereafter phase inverting
said extruded hollow-fiber in said bath containing only water to
form said hollow-fiber.
15. The method of claim 12, further comprising replacing steps (c)
through (f) by the following steps: mixing said second amount of
said primary solvent with an amount of water to form said bore
liquid; extruding an amount of said first solution and an amount of
said bore liquid through said spinneret to produce said extruded
hollow-fiber; subjecting said extruded hollow-fiber to a bath
containing an amount of said chlorinated aqueous amine solution;
and thereafter phase inverting said extruded hollow-fiber in said
bath containing only water to form said hollow-fiber.
16. The method of claim 12, wherein said polymer is selected from
the group consisting of polyvinylidene fluoride,
polytrifluoroethylene, polychlorotrifluoroethylene, fluorinated
ethylene propylene, polyhexafluoropropylene, and combinations
thereof.
17. The method of claim 12, wherein said primary solvent is
selected from the group consisting of N-methyl-2-pyrrolidone,
N,N-dimethylacetamide, N,N-dimethylformamide, dimethylsulfoxide,
hexamethyl phosphoramide, tetramethylurea, triethyl phosphate,
trimethyl phosphate, acetone, methyl ethyl ketone, tetrahydrofuran,
and combinations thereof.
18. The method of claim 12, wherein said amine solvent is selected
from the group consisting of methylamine, ethylamine,
isopropylamine, propylamine, dimethylamine, diethylamine,
diisopropylamine, dipropylamine, trimethylamine, triethylamine,
tripropylamine, and combinations thereof.
19. The method of claim 12, wherein said chlorine source is
selected from the group consisting of chlorine gas, hypochlorite,
and combinations thereof.
Description
BACKGROUND OF THE INVENTION
Water is the origin of every living thing. Yet the function of
water--as a lubricant or a solvent, a displacing fluid or a
displaced fluid, a wetting fluid or a non-wetted fluid, to name a
few--firmly lies at the heart of physical situations that vary from
geology (e.g., altering miscibility and interfacial forces),
through biology (e.g., de-toxifying wastewater and derivative
streams of wastewater), to oceanology (e.g., inverting the salinity
of seawater to produce potable water and brine).
In saline water desalination, membrane distillation (MD) offers an
elegant alternative concept to conventional methods [e.g.,
multi-stage flash (MSF) desalination, multi-effect (ME)
distillation, and reverse osmosis (RO)], as energy efficient
especially when combined with low grade or waste energy sources. MD
has an essential simplicity of structure in that it consists
inherently only of a compact housing envelop and a type of a low
pressure separating surface performing only one function between
two fluids at relatively moderate temperatures (e.g.,
<90.degree. C.). However, vapor permeability through MD
membranes is low; thereby enhancing it is of vital interest.
THE OBJECTIVES OF THE INVENTION
The main objective of this invention is to provide membranes that
can be extremely water non-wet and extremely permeable to wetting
fluids including vapor.
BRIEF SUMMARY OF THE INVENTION
The present invention generally provides methods for preparing a
material for casting a flat-sheet, extruding a solid-fiber, and/or
extruding a hollow-fiber utilizing a chlorinated aqueous amine
solution as an effective solvent for phase inverting the material
to form a crystalline polymorph structure.
The inventive materials are not restricted to use in connection
with one particular application. They can be used, in general, to
separate water vapor from saline water in MD, to separate gases and
hydrophobic constituents from wastewater, to separate gases and/or
oil from wet oil. Further objects, novel features, and advantages
of the subject invention will be apparent to those skilled in the
art upon examining the accompanying drawings and upon reading the
following description of the preferred embodiments, or may be
learned by practice of the invention. Those of ordinary skills in
the art will appreciate that the subject invention can be modified
or adapted in a variety of ways. All such modifications or
adaptions, which fall within the scope of the appended claims, are
intended to be covered.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates surface tensions of the aqueous amine (TMA)
solution.
FIG. 2A illustrates the steps to prepare a material for casting a
flat-sheet.
FIG. 2B illustrates the effect an aqueous amine solution on
changing water contact angles of a membrane.
FIG. 2C illustrates another set of steps to prepare a material for
casting a flat-sheet.
FIG. 3A illustrates the steps to prepare a material for extruding a
solid-fiber.
FIG. 3B illustrates another set of steps to prepare a material for
extruding a solid-fiber.
FIG. 4A illustrates the steps to prepare a material for extruding a
hollow-fiber.
FIG. 4B illustrates another set of steps to prepare a material for
extruding a hollow-fiber.
FIG. 4C illustrates a further set of steps to prepare a material
for extruding a hollow-fiber.
FIG. 4D illustrates yet a further set of steps to prepare a
material for extruding a hollow-fiber.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The Relative Non-Wettability
Phase inversion has been appeared in a multitude of forms, but all
have been characterized by specific controls of composition (e.g.,
solubility, pH, etc.), temperature, pressure, and/or combinations
thereof. Phase inversion is also used as an enabling step in the
work-up or break-up of a reaction or an interaction, before final
displacement of a phase, before final casting or extruding of a
phase, or before final separation/purification of a phase or a
product by distillation, filtration, sublimation, precipitation,
crystallization, adsorption, absorption, among others.
Precipitation, for example, involves phase inversion, wherein a
soluble species in a primary solvent is transformed into an
insoluble state either by decreasing its solubility in the primary
solvent or by extracting the primary solvent from the soluble
species. One form is selective precipitation, which stands on
inducing a secondary solvent to a solution to reduce the solubility
of the species by binding the primary solvent to the secondary
solvent. Of course, the identity of the primary solvent, the nature
and concentration of the soluble species and the conditions under
which phase inversion is conducted come into play, but the
effectiveness resides with the identity and modification of the
secondary solvent.
The induction of an amine solvent [e.g., methylamine (ME),
ethylamine (EA), isopropylamine (IPA), propylamine (PA),
dimethylamine (DMA), diethylamine (DEA), diisopropylamine (DTA) and
dipropylamine (DPA)] has been innovatively used by the inventor as
a secondary solvent in a liquid phase precipitation as well as a
vapor (compressed and/or flashed) phase precipitation with multiple
variants to effectively selectively precipitate targeted: (1)
inorganic species; and/or (2) ionizable organics (e.g., carboxylic
salts, phenol salts, etc.) and inorganics (e.g., carbonates,
sulfides, etc.) from aqueous streams. The yields of these
precipitation variants are remarkable particularly, for example,
in: (1) de-scaling saline streams; (2) aiding the de-oiling of
saline streams; (3) de-mixing the amphiphilic portion of wet oil;
and (4) de-folding the amphiphilic nature of proteins in wastewater
to ultimately separate endotoxins with dense gas (e.g., carbon
dioxide).
The key factors in these selective precipitation variants are that
the amine solvent (the secondary solvent) is miscible with water
(the primary solvent), whereas: (1) the solubility of the targeted
inorganic species is very limited in the amine solvent; and/or (2)
the ionizablity of targeted organic and inorganic species in the
presence of the amine solvent becomes crossover (below or above)
the neutral pH. The latter has been further modified by, for
example, transforming the amine solvent into an anionated form by
reacting it with acid, since these amine solvents are weak bases
that undergo reversible reactions with water or acid to form weak
acids, and then regenerating the amine solvent (a weak base) from
its anionated form by an external hydroxide source (an inorganic or
organic). The external hydroxide source serves, in turn, a
multitude of purposes including restoring the amine solvent to its
weak basic form to serve a further purpose, facilitating the
recovery of the amine solvent for reuse, and using the external
hydroxide source, itself, in a further step (e.g., de-scaling).
This pH switchability of the amine solvent displaces selectively
the ionization equilibrium of reactive species towards either their
molecular forms or ionized states. It displaces the ionization
equilibrium of, for example, carboxylic acids and phenols in wet
oil towards their molecular forms under an acidic condition, which
are essentially hydrophobic instead of their amphiphilic ionized
states under slightly basic conditions. The opposite goes for
naturally occurring basic constituents in wet oil. The pH
switchability thus leads to two low values of wet oil interfacial
tension; one at either end of the pH scale.
As such, the inventor has innovatively exploited the competition
between targeted inorganic species and/or ionizable species and
amine molecules on the water molecules by: (1) the "amining out"
step wherein targeted inorganic species are precipitated whereas
the amine solvent remains in solution; (2) "salting out" step
wherein an amine solvent is separated while inorganic species
remains in the solution; (3) the "ionizing out" step wherein acidic
and basic ionizable organic and inorganic species and proteins are
reversibly selectively displaced by dissolving them, precipitating
them, isolating them, and/or converting them to a gaseous state
whereas the amine solvent remains in solution; (4) the "wetting
out" step wherein a membrane's pores are selectively filled with a
liquid phase or fluid; and/or (5) the standalone, sequential or
simultaneous occurrence of such described steps. The fundamental
thermodynamic frameworks for the precipitation of ionic species in
mixed solvents have also been established [Bader; 1998 and
1999].
Phase inversion by inducing a secondary solvent has also long been
used, among other concepts (e.g., melting, sintering, etching,
stretching, surface coating, surface grafting, etc.), to prepare
membranes. In a conventional polymer phase inversion process
comprising three components, a polymer is dissolved in a primary
solvent to form a homogenous solution. The polymer is then
precipitated from the homogenous solution by a secondary solvent,
wherein the secondary solvent is soluble in the primary solvent
while the polymer is nearly insoluble in the secondary solvent.
During phase de-mixing, the solution is cast (e.g., flat-sheet) or
extruded (e.g., hollow-fiber, tubular, etc.) into a desired shape,
wherein the polymer-rich phase solidifies into a membrane matrix
whereas the polymer-poor phase develops into pores within the
membrane. The thermodynamic principle for the precipitation of
polymeric species in mixed solvents has been delineated [e.g., Hsu
and Prausnitz, 1974]. In different variants of inducing a secondary
solvent, polymer phase inversion by precipitation has been used to
prepare membranes. The basic principles of these variants are
briefly summarized in the following paragraph [e.g., Ferry,
1936].
A membrane film was historically practically prepared by subjecting
a polymer dissolved in a primary solvent to vapor of a secondary
solvent to prevent the evaporation of the primary solvent from the
formed film but allow the vapor of the secondary solvent to diffuse
into the formed film, thereby forming a porous membrane without a
top layer. Here, the secondary solvent is more volatile than the
primary solvent. In another variant, a polymer is dissolved in
mixed primary and secondary solvents, wherein the primary solvent
is more volatile than the secondary solvent, whereby increasing the
content of the polymer and secondary solvent by evaporating the
primary solvent, which eventually leads to polymer precipitation
resulting in forming a skinned membrane. In a further variant, a
polymer is dissolved in a primary solvent, and the homogenous
solution is cast on a substrate by dip coating or spraying,
followed by allowing the primary solvent to evaporate in an inert
atmosphere (e.g., nitrogen or air) to expel the vapor of the
primary solvent, thereby forming a dense homogenous membrane. Phase
inversion by these evaporative precipitation variants has been
further adapted to prepare membranes by liquid-phase precipitation,
wherein a homogenous solution comprising a polymer and a primary
solvent is directly immersed in a bath containing a secondary
solvent [e.g., Loeb and Sourirajan, 1963]. The latter made the
practical use of reverse osmosis (RO) hydrophilic membranes to
desalinate seawater possible, which was a landmark contribution of
United States to the desalination field. Membrane fabrications
since then remain essentially extensions of such methods; all which
involve melting or dissolving a polymer, casting or extruding the
melted or dissolved polymer, and precipitating the polymer by phase
inversion; but again the effectiveness resides with the identity
and modification of the secondary solvent.
Precedent surface modification methods for polytetrafluoroethylene
(PTFE) to make it bondable to other materials by reacting the
surface with suitable fluid cation/metal reactants before bonding
were developed in the 1950s [U.S. Pat. No. 2,789,063]. The methods
were based on replacing fluorine in the surface layer of PTFE with
the cation or metal, thereby making the surface more hydrophilic.
Alkali cations (e.g., sodium), alkaline earth cations (e.g.,
calcium), and transition metals (e.g., manganese or zinc) were used
to react with PTFE surfaces at high temperatures [e.g., above the
melting point of the cation or metal, but below the melting point
of PTFE (315.degree. C.)] or heating the PTFE material as it
emerged from a liquid reacting bath at high temperatures (e.g.,
220.degree. C.); wherein the cation or metal is a vapor, a cation
or metal hydride, or in non-aqueous liquid ammonia or methylamine.
It should also be noted that, as all hydroflurocarbon polymers,
pyrolysis at high temperatures also degrades PVDF by the evolution
of a large amount of hydrogen fluoride (HF). This large loss of HF,
de-hydrofluorination, is due to the equal distribution of repeated
hydrogen-fluoride chains in PVDF. De-hydrofluorination may be
followed by the formation of double bonds (chain scission, thereby
more thermal stability), and/or may result in cross-linking of the
polymer (fusing, thereby highly orientated fibrils and better
mechanical strength). The de-hydrofluorination mechanisms of PVDF
by pyrolysis may be expressed as follows [Madorsky, 1964].
##STR00001##
Chemically, rather than thermally, cross-linking modifications of
PVDF and/or equivalent materials to produce highly orientated
interlinked semi-crystalline particle or globular structures is the
underpinning objective of this invention. This can be achieved
without replacing fluorine from the surface layer of a
hydroflurocarbon polymer at high temperatures or degrading the bulk
of the hydroflurocarbon polymer by pyrolysis. Thus, this invention
provides methods for obtaining desired surface effects of PVDF or
equivalent materials, which will now be explained by several points
and illustrated by various non-limitative embodiments.
First, PVDF possesses two valuable properties of practical
importance, which are the polymorphic and piezoelectric properties.
In regards to the polymorphic properties, PVDF is a border line
hydrophobic (Table 1) semi-crystalline polymer that is
approximately 50% amorphous; wherein the monomer's structure is
[--CH.sub.2--CF.sub.2--], and the repeated chains occur mostly in a
head to tail configuration. PVDF can be dissolved at low
temperatures (e.g., <60.degree. C.) in an organic solvent (as a
primary solvent) such as N,N-dimethylacetamide (DMA),
N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), hexamethyl
phosphoramide (HMPA), N-methyl-2-pyrrolidone (NMP), tetramethylurea
(TMU), triethyl phosphate (TEP), trimethyl phosphate (TMP),
acetone, methyl ethyl ketone (MEK), tetrahydrofuran (THF), and/or
combinations thereof. This is unlike some hydroflurocarbon polymers
such as PTFE (Teflon) or other hydrophobic plastic materials such
as polyethylene (PE) and polypropylene (PP). Because of its
solubility in such solvents, the fabrication of PVDF membranes via
wet, rather than melt, phase inversion methods is possible. Since
PVDF is insoluble in water, the repeatedly reported medium (e.g.,
as a secondary solvent) for fabricating PVDF via phase inversion is
usually water with or without peroxy compounds (e.g., containing
the divalent group O--O) acting as polymerization catalysts. In
regards to the piezoelectric properties (e.g., transfer mechanical
energy to electrical energy and vice versa), the high Curie point
(103.degree. C.; the temperature above which the piezoelectric
effect breaks down), and the response to an electric potential by
acting along the backbone make PVDF a valuable material. Other
useful properties of PVDF include high elastic modulus and high
rigidity (resists deformation); resistance to heat, combustion,
ageing and abrasion; chemically inert and non toxic; and stability
to radiation (X-ray, UV and Gamma).
Second, one of the utilities of the polymorphic properties of PVDF
is to form membranes. Recalling that a raw polymer must be soluble
in a primary solvent, and, in turn, the primary solvent must be
soluble in a secondary solvent, whereas the polymer is insoluble in
the secondary phase; thereby de-mixing the polymer, as it is forced
out of the primary solvent by the secondary solvent, into a
polymer-rich phase and a surrounding polymer-lean solution.
However, the polymer-rich phase may be dominated by amorphous
particles (precipitation), pure crystalline polymorph particles
(crystallization), or a concurrent combination of precipitation and
crystallization. The differences among them lie in the formation
process and the final product formed. As is the nature of this type
of phase inversion, the formation process (the thereby predominance
of either one) requires a proper effective secondary solvent and a
precise control over the conditions (e.g., the rate of
induction-time as related to instant or delayed de-mixing, and the
rate of mass transfer as related to the level of saturation and
stability) under which the thermodynamic and kinetic phase
behaviors of the forming membrane are dictated. In this invention,
crystallization of PVDF or an equivalent material is sought out to
form effective and inexpensive membranes.
Third, amine solvents [including methylamine (ME), ethylamine (EA),
isopropylamine (IPA), propylamine (PA), dimethylamine (DMA),
diethylamine (DEA), diisopropylamine (DIPA), dipropylamine (DPA),
trimethylamine (TMA), triethylamine (TEA), tripropylamine (TPA)]
are unexpectedly found to be effective in crystallizing PVDF or an
equivalent material to form the sought out membranes and other
articles. Such amine solvents are weak bases, which do not generate
hydroxyl ions directly by dissociation, but by reaction with water.
For example, IPA reacts with water as follows:
CH.sub.3CH.sub.2CH.sub.2NH.sub.2+H.sub.2O.revreaction.CH.sub.3CH.sub.2CH.-
sub.2NH.sub.3.sup.+OH.sup.- (2) Yet, most weak bases are anions.
For example, the fluoride ion is a weak base anion, which undergoes
a similar reversible reaction with water as follows:
F.sup.-+H.sub.2O.revreaction.HF+OH.sup.- (3) In both cases of such
weak bases, the forward reactions occur only to a slight extent to
produce a weak acid (e.g., CH.sub.3CH.sub.2CH.sub.2NH.sub.3.sup.+;
HF); and an enough OH.sup.- ion to make the solution basic.
Further, the reaction of the amine solvent (IPA for example) with
hydrofluoric acid generates the amine solvent in an anionated form
as follows:
CH.sub.3CH.sub.2CH.sub.2NH.sub.2+HF.fwdarw.CH.sub.3CH.sub.2CH.sub.2NH.sub-
.3.sup.+F (4) Here, the novelty of this invention resides with the
use of an aqueous amine solvent as a weak base, thereby not as a
strong denature, to pre-treat a solution of PVDF (or an equivalent
material) dissolved in a primary solvent before phase inverting the
solution; wherein the aqueous amine solvent gently draws some of
the inorganic fluorine from the water-insoluble PVDF polymer for
reaction, thereby generating the hydrofluoric acid by
de-hydrofluorinating the PVDF; wherein implicit in this
pre-treatment is the further reaction of the generated hydrofluoric
acid with the aqueous amine solvent to regenerate the amine solvent
in the anionated (fluorine) form; and wherein the amine solvent in
the anionated form, as a weak anion base, represents a further step
that draws in an essentially similar manner some of the fluorine
from the water-insoluble PVDF polymer; thereby OH.sup.- ions are
dissociated from the aqueous amine solvent, the released fluorine
anion from PVDF and the amine solvent in the anionated form to
diffuse in the PVDF polymer and bring it to reaction. The combined
effects of the aqueous amine solvent and the amine solvent in the
anionated form, which are not strong denaturants, minimize the
disruption of inter-molecular interactions in PVDF (or an
equivalent material), and leads to the formation of very fine
crystalline clusters. The implication of this novelty of molecular
interactions is that they serve as gentle re-crystallization media
prior to phase inverting the PVDF solution.
Fourth, Table 2 presents the liquid surface tensions of water and
the amine solvents. The liquid surface tensions (.sigma..sub.L) of
such amine solvents are not only much lower than .sigma..sub.L of
water (Table 2), but also lower than the critical surface tension
(.sigma..sub.C) of PVDF (Table 1). Here, .sigma..sub.C is the
surface tension at which a liquid just completely wets a surface
(.theta.=0). The ability of such an aqueous amine solvent to spread
through the low energy PVDF solution depends on the volume fraction
of the amine solvent in water to depress the surface tension of
water (.sigma..sub.L) in the aqueous amine solution (.sigma..sub.S)
preferably below .sigma..sub.C of PVDF. For example, .sigma..sub.L
of C.sub.3H.sub.9N [Table 2; (TMA: 13.4 mN/m; IPA: 17.5 mN/m)] is
roughly about half .sigma..sub.C of PVDF [Table 1; (31.6 mN/m)].
FIG. 1 shows the surface tensions of the aqueous TMA solution as a
function of volume fractions, and an essentially similar trend is
exhibited by the aqueous IPA solution. Here, the volume fraction
(.phi.) is defined as follows [Bader, 1999]:
.phi..times..nu..times..times..nu. ##EQU00001## where x.sub.i is
the mole fraction and v.sub.i is the pure solvent molar volume. A
relatively small volume fraction of most of such amine solvents
would thus reduce the interfacial tension of the aqueous amine
solution to about or below .sigma..sub.C of PVDF. It follows from
the definition of .sigma..sub.C and the insolubility of PVDF in
pure water that the novelty of this invention further resides in
sufficiently lowering the surface tension of water in the aqueous
amine solution by the amine solvent; thereby largely delaying the
instantaneous de-mixing (precipitation) power of pure water prior
to phase inverting the PVDF solution.
Fifth, the pores in a hydrophobic membrane are filled with the
fluid that wets the membrane. The non-wetting fluid (water) does
not permeate into pores of the membrane as long as the pressure on
the non-wetting fluid side is kept below a critical value, which is
known as the "liquid entry" or "breakthrough" pressure. For
gas-liquid contacting (e.g., vapor-water as in MD) or liquid-liquid
extraction (e.g., de-mixing oil and water phases from wet-oil), the
"liquid entry" pressure of water (the non-wetting fluid) may be
roughly approximated as follows:
.DELTA..times..times..times..sigma..times..times..theta.
##EQU00002## where .sigma. may refer to as the surface tension in
the case of vapor-liquid contacting or the interfacial tension in
the case of liquid-liquid contacting, .theta..sub.w is the water
contact angle of the membrane, and r is the pore radius of the
membrane. Eq. (6) implies that the higher the water contact angle
and the lower pore radius of the membrane, the higher is the liquid
entry pressure of water. It follows from the definition of
.DELTA.P.sub.E and the insolubility of PVDF in pure water that the
novelty of this invention yet further resides in substantially
increasing the water contact angle of the membrane by the aqueous
amine solution and substantially decreasing the pore size of the
membrane by limiting the water content in the aqueous amine
solution prior to phase inverting the PVDF solution.
FIG. 2A depicts one embodiment of this invention, wherein an
aqueous amine solution is utilized as a useful solvent in the
polymer phase inversion method to form membranes in a flat-sheet
configuration. As such, an amount of a polymer [P] is dissolved in
an amount of a primary solvent [1A] to form a homogeneous first
solution [FS]. An amount of an amine solvent [2A] is mixed with an
amount of water [3A] to form an aqueous amine solution [AAS] to
reduce .sigma..sub.S of the aqueous amine solution [AAS] to
preferably about or below .sigma..sub.C of PVDF. An amount [10] of
the aqueous amine solution [AAS], which now serves as a second
solvent, is then mixed with an amount [FS1] of the first solution
[FS] to control the crystal growth of the polymer [P] by conceiving
near induction nuclei; thereby obtaining a readily tailored
structural second solution [SS]. An amount of the second solution
[SS1] is then casted on a substrate [SC], wherein this amount [SS1]
controls the thinness of the casted second solution [SS] on the
substrate. The casted substrate [SC] is phase inverted [PI] in a
bath containing only water [3B] at a temperature preferably in the
range of 5-25.degree. C. The substrate containing the attached
phase inverted membrane is removed from the bath; wherein the
attached membrane is spontaneously veered away from the substrate
as the flat sheet membrane, rinsed with water and dried by the
atmospheric air (these latter steps are not shown in FIG. 2A).
The hydroflurocarbon polymer [P] is selected from the group
consisting of polyvinylidene fluoride (PVDF), polytrifluoroethylene
(PFE), polychlorotrifluoroethylene (PCFE), fluorinated ethylene
propylene (FEP), polyhexafluoropropylene (PHFP), and/or
combinations thereof.
The primary solvent to dissolve the polymer is selected from the
group consisting of N-methyl-2-pyrrolidone (NMP),
N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF),
dimethylsulfoxide (DMSO), hexamethyl phosphoramide (HMPA),
tetramethylurea (TMU), triethyl phosphate (TEP), trimethyl
phosphate (TMP), acetone, methyl ethyl ketone (MEK),
tetrahydrofuran (THF), and/or combinations thereof.
The amine solvent to form the aqueous amine solution is selected
from the group consisting of methylamine (ME), ethylamine (EA),
isopropylamine (IPA), propylamine (PA), dimethylamine (DMA),
diethylamine (DEA), diisopropylamine (DTPA), dipropylamine (DPA),
trimethylamine (TMA), triethylamine (TEA), tripropylamine (TPA),
and/or combinations thereof.
Thus, successful flat-sheet membranes were made according to this
invention in a multitude of variants. For example, in one variant,
a PVDF powder (as a polymer [P]) and NMP (as a primary solvent
[1A]) were mixed to form a homogenous first solution [FS] (3 vol %
[P]: 97 vol % [1A]). IPA [2A] and water [3A] were mixed to form an
aqueous amine solution [AAS]; wherein .phi. of IPA in water was
about 0.23 (about 6 mol %), which corresponded to about 31.1 mN/m
of .sigma..sub.L the aqueous amine solution. Different amounts [10]
of the aqueous amine solution [AAS] were then mixed with fixed
amounts [FS1] of the first solution [FS] to form several second
solutions [SS]. Each of the second solutions was casted on an inert
substrate, each of the casted substrate was immersed in a bath
containing only water for phase inversion, and each of the formed
flat-sheet membranes is removed from each substrate and washed with
water. FIG. 2B shows the water contact angle for each of the
flat-sheet membrane as a function of the volume ratio
(V.sub.r=V.sub.l/V.sub.FS1), where the latter is the volume of the
aqueous amine solution (V.sub.1) to the volume of the first
solution (V.sub.FS1). The water contact angle (.theta..sub.w)
increased (88-161.5.degree.) with increasing V.sub.r, wherein a
plateau is reached at higher V.sub.r values. The oil contact angle
(.theta..sub.o) practically approached zero; thereby oil would wet
the membrane and spread freely over the membrane surface at a rate
depending on the viscosity of oil and the roughness of the membrane
surface. The cross-section and surface morphology of the membrane,
as observed by scanning electron microscopy, revealed that the
membrane surface is skinless, rough and with a structure comprising
packed interconnected spherulitic particles. The structural ratio
of fluorine to carbon in the original PVDF is reduced by roughly
17% in the PVDF membranes upon the addition of the aqueous amine
solutions (V.sub.r=0.02); which indicated that: (1) the chemical
modification of PVDF by the aqueous amine solution took place, as
essentially described in Paragraphs [0029] and [0030], thereby
chemically de-hydrofluorinating the PVDF at essentially ambient
temperature, instead of thermally at high temperatures, and in an
essentially equivalent manner as given in Eq. (1B); and (2) the
exhibited .theta..sub.w plateau at higher V.sub.r values (>0.02)
revealed that the de-hydrofluorination of PVDF reached levels that
would be structurally detrimental (e.g., lower the mechanical
strength) to an unsupported thin flat-sheet membrane. The
crystalline structure of the membranes, as observed by X-ray
diffraction, revealed that the degree of crystallinity increased
with increasing V.sub.r with patterns corresponded to the .beta.
crystalline phase of PVDF. This is consistent with the phase
inversion approach in this invention since the .beta. crystalline
phase formed from wet PVDF, which it has actually more
intermolecular stability. The structure of .beta. phase forces the
fluorine atoms along the carbon backbone to come closer together,
which allows tighter packing density and reduces the intermolecular
strain, thereby allowing greater chain interconnectivity and more
dipolar alignment giving the PVDF membrane its strong piezoelectric
properties. Such very desirable properties would come into play in
applying an electrical field to the PVDF membrane (if needed).
However, a suitable membrane for MD to separate water vapor from a
saline stream should exhibit high vapor permeability, which may be
obtained by making the pore size of the membrane relatively
larger.
When chlorine is introduced into water; as chlorine gas (Cl.sub.2),
hypochlorite (ClO.sup.-) in the form of sodium or calcium, or in
other forms, it rapidly undergoes hydrolysis to produce mainly
hypochlorous acid (HClO); wherein the latter is a weak acid that
dissociates in aqueous solution as follows:
HClO+H.sub.2O.revreaction.ClO.sup.-+H.sup.++H.sub.2O (7) If an
amine solvent (IPA for example) is reacted with hypochlorous acid,
it will generate the amine solvent in a monochloroamine form as
follows:
CH.sub.3CH.sub.2CH.sub.2NH.sub.2+HClO.fwdarw.CH.sub.3CH.sub.2CH.sub.2NHCl-
+H.sub.2O (8) If the source of chlorine is chlorine gas, the
hydrolysis of the chlorine gas will also produce hydrochloric acid
in addition to the dominant hypochlorous acid. The amine solvent
(IPA for example) also reacts with hydrochloric acid to regenerate
the amine solvent in an anionated form as follows:
CH.sub.3CH.sub.2CH.sub.2NH.sub.2+HCl.fwdarw.CH.sub.3CH.sub.2CH.sub.2NH.su-
b.3.sup.+Cl (9) In addition to utility of an aqueous amine solution
as described in Paragraphs [0029] and [0030], the novelty of this
invention further resides with the use of a chlorinated aqueous
amine solvent (e.g., CH.sub.3CH.sub.2CH.sub.2NHCl) to serve as a
pore enlarger; thereby enhancing the vapor permeability of PVDF or
an equivalent material.
FIG. 2C depicts another embodiment of this invention, wherein a
chlorinated aqueous amine solution is utilized as a useful solvent
in the polymer phase inversion method to form membranes in a
flat-sheet configuration. The processing steps as shown in FIG. 2C
differ from the processing steps as shown in FIG. 2A in that: (1)
an amount of an amine solvent [2A], an amount of water [3A], and an
amount of a chlorine source [4] are mixed together to form the
chlorinated aqueous amine solution [AAS]; and (2) an amount [10] of
the chlorinated aqueous amine solution [AAS] is mixed with an
amount [FS1] of the first solution [FS] to form the second solution
[SS].
The chlorine source is selected from the group consisting of
chlorine gas, hypochlorite, and/or combinations thereof.
A flat-sheet configuration is very useful in different applications
including, for example, replacing conventional coalescing packings
of a 3-phase separator in an oil gathering center by the invented
flat-sheets in submerged membrane modules to effectively directly
simultaneously separate gas and oil from water within the 3-phase
separator, wastewater membrane bioreactors, among other
applications. A solid-fiber configuration utilizing the
piezoelectric property of PVDF is very useful in different
applications including, for example, energy harvesters (e.g., solar
panels), mechanical actuators, strain sensors, artificial muscles,
and nearly completely non-porous membranes for higher pressure
applications. A hollow-fiber configuration is also very useful in,
for example, a gas-liquid or a liquid-liquid contactor especially
for standalone membrane applications. However, the three essential
formation differences among these configurations are morphology,
viscosity, and tension/stress. For a flat-sheet configuration or a
solid-fiber configuration, morphology adjustments start naturally
from the outer surface of a cast or extrude film after immersing in
a phase inverting bath. For a hollow-fiber configuration,
morphology adjustments are simultaneously required for the inner
(lumen side) and the outer (shell side) surfaces, wherein the inner
surface is controlled by a bore fluid (e.g., liquid or gas) as an
internally phase inverting media, and wherein the outer surface is
controlled by a solvent in an externally phase inverting bath. The
required viscosity for a polymer solution (a dissolved polymer in a
primary solvent) for spinning a solid-fiber or a hollow-fiber may
be an order of magnitude higher than that for casting a flat-sheet;
thereby the required amount of the polymer for the solid-fiber or
the hollow-fiber may be in the order of 3-times the required amount
for the flat-sheet. Unlike the formation of the flat-sheet, the
solid-fiber or the hollow-fiber is usually formed under tension
and/or stress.
FIG. 3A depicts a further embodiment of this invention, wherein a
chlorinated aqueous amine solution is utilized as a useful solvent
in the polymer phase inversion method to form membranes in a
solid-fiber configuration. An amount of a polymer [P] is dissolved
in an amount of a primary solvent [1A] to form a homogeneous first
solution [FS]. An amount of an amine solvent [2A], an amount of
water [3A], and an amount of a chlorine source [4] are mixed
together to form the chlorinated aqueous amine solution [AAS]. An
amount [10] of the chlorinated aqueous amine solution [AAS] is
mixed with an amount [FS1] of the first solution [FS] to form a
second solution [SS]. An amount [SS1] of the second solution [SS]
is extruded through a spinneret [30]. At the exit of the spinneret,
conceived fibers [50] may pass through an air gap [40] before
entering a first spinning bath [60] containing only water [3B] for
phase inverting at a temperature preferably in the range of
5-25.degree. C. After the first spinning bath [60], the
pre-solidified solid-fiber is wound to the first roller [R1], and
then it is exposed to a second bath [60A] containing also only
water for washing and a further solidification, wherein a second
drafting occurs between the first roller [R1] and a second roller
[R2]. The second drawing mostly solidifies the solid-fiber, and if
needed, freeze drying or hot air drafting may be applied (not shown
in FIG. 3A) to the spun solid-fiber [50A] prior to winding.
FIG. 3B depicts yet a further embodiment of this invention, wherein
a chlorinated aqueous amine solution is utilized as a useful
solvent in the polymer phase inversion method to form membranes in
a solid-fiber configuration; which differs from FIG. 3A in that:
(1) an amount [FS1] of the first solution [FS] is extruded through
the spinneret [30]; and (2) an amount [10] of the chlorinated
aqueous amine solution [AAS], instead of only water, is used in the
first spinning bath [60], before phase inverting the extruded
solid-fiber in the second bath [60A] that contains only water to
form the solid-fiber.
FIG. 4A depicts yet a further embodiment of this invention, wherein
a chlorinated aqueous amine solution is utilized as a useful
solvent in the polymer phase inversion method to form membranes in
a hollow-fiber configuration. An amount of a polymer [P] is
dissolved in a first amount of a primary solvent [1A] to form a
homogeneous first solution [FS]. An amount of an amine solvent
[2A], an amount of water [3A], and an amount of a chlorine source
[4] are mixed together to form the chlorinated aqueous amine
solution [AAS]. A first amount [10A] of the chlorinated aqueous
amine solution [AAS] is mixed with an amount [FS1] of the first
solution [FS] to form a second solution [SS], which serves as an
external coagulant to control the morphology of the outer surface
of the hollow fiber. A second amount [10B] of the chlorinated
aqueous amine solution [AAS] is mixed with a second amount of the
primary solvent [1B] to form a bore liquid [BL], which serves as an
internal coagulant to reduce the resistance and control the
morphology of the inner surface of a hollow fiber. An amount [SS1]
of the second solution [SS] and an amount [20] of the bore liquid
[BL] are extruded through a spinneret [30]. At the exit of the
spinneret, conceived fibers [50] pass through an air gap [40]
before entering a first spinning bath [60] containing only water
[3B] for phase inverting at a temperature preferably in the range
of 5-25.degree. C. After the first spinning bath [60], the
pre-solidified hollow-fiber is wound to the first roller [R1], and
then it is exposed to a second bath [60A] containing also only
water for washing and a further solidification, wherein a second
drafting occurs between the first roller [R1] and a second roller
[R2]. The second drawing mostly solidifies the hollow fiber, and if
needed, freeze drying or hot air drafting may be applied (not shown
in FIG. 4A) to the spun hollow-fiber [50A] prior to winding.
FIG. 4B depicts yet a further embodiment of this invention, wherein
a chlorinated aqueous amine solution is utilized as a useful
solvent in the polymer phase inversion method to form membranes in
a hollow-fiber configuration; which differs from FIG. 4A in that
the second amount of the primary solvent [1B] is mixed with an
amount of water [3C], instead of the second amount of the
chlorinated aqueous amine solution [10B], to form the bore liquid
[BL].
FIG. 4C depicts yet a further embodiment of this invention, wherein
a chlorinated aqueous amine solution is utilized as a useful
solvent in the polymer phase inversion method to form membranes in
a hollow-fiber configuration; which differs from FIG. 4A in that:
(1) an amount [FS1] of the first solution [FS] and an amount [20]
of the bore liquid [BL] are extruded through the spinneret [30];
and (2) the first amount [10A] of the chlorinated aqueous amine
solution [AAS] is used, instead of only water, in the first
spinning bath [60], before phase inverting the extruded
hollow-fiber in the second bath [60A] that contains only water to
form the hollow-fiber membrane.
FIG. 4D depicts yet a further embodiment of this invention, wherein
a chlorinated aqueous amine solution is utilized as a useful
solvent in the polymer phase inversion method to form membranes in
a hollow-fiber configuration; which differs from FIG. 4A in that:
(1) the second amount of the primary solvent [1B] is mixed with the
amount of water [3C], instead of the second amount of the
chlorinated aqueous amine solution [10B], to form the bore liquid
[BL]; (2) an amount [FS1] of the first solution [FS] and an amount
[20] of the bore liquid [BL] are extruded through the spinneret
[30]; and (3) an amount [10] of the chlorinated aqueous amine
solution [AAS] is used, instead of only water, in the first
spinning bath [60], before phase inverting the extruded
hollow-fiber in the second bath [60A] that contains only water to
form the hollow-fiber membrane.
The above described inventive methods of utilizing an aqueous amine
solution or a chlorinated aqueous amine solution are aimed at
semi-crystalline polymers; wherein fine crystal clusters are
selectively and relatively slowly formed from a polymer dissolved
in a primary solvent by such amine solutions resulting in
crystalline polymorph structures. Generated hydrophilic membranes
by phase inverting glassy polymers (e.g., polysulfone, cellulose
acetate, regenerated cellulose, nitrocellulose, polyamide,
polyimide, etc.) usually involved very rapid precipitation
resulting in amorphous macro-void structures. However, the
utilization of an aqueous amine solution or a chlorinated aqueous
amine solution as described in this invention can be extended to
such glassy polymers to form membranes with the structures free of
such undesirable macro-voids.
TABLE-US-00001 TABLE 1 Critical Surface Tensions (.sigma..sub.c)
and Water Contact Angles (.theta..sub.w). .sigma..sub.c
.theta..sub.w Material (mN/m) (.degree.) Polyvinylidene fluoride
(PVDF) 31.6 89 Polytrifluoroethylene (PFE) 26.5 92
Polychlorotrifluoroethylene (PCFE) 30.8 99.3 Fluorinated ethylene
propylene (FEP) 19.1 108.5 Polytetrafluoroethylene (PTFE) 19.4 112
Polyhexafluoropropylene (PHFP) 16.9 112
TABLE-US-00002 TABLE 2 Selected Properties of Solvents.
.sigma..sub.L MV BP VP .rho. .mu. Solvent (mN/m) (A.sup.3)
(.degree. C.) (mmHg) (g/cm.sup.3) (cp) Water (H.sub.2O) 71.9 30.0
100.0 23.6 0.998 0.76 MA (CH.sub.5N) 19.2 73.4 -6.4 2,680.1 0.703
0.19 DMA (C.sub.2H.sub.7N) 26.3 114.1 6.9 1,475.3 0.656 0.21 TMA
(C.sub.3H.sub.9N) 13.4 155.1 3.0 1,699.2 0.633 0.32 EA
(C.sub.2H.sub.7N) 19.1 109.6 16.6 1,062.2 0.683 0.24 DEA
(C.sub.4H.sub.11N) 19.9 171.8 55.5 235.7 0.707 0.33 TEA
(C.sub.6H.sub.15N) 20.2 230.8 89.6 67.7 0.728 0.34 IPA
(C.sub.3H.sub.9N) 17.5 142.7 32.4 575.1 0.688 0.36 PA
(C.sub.3H.sub.9N) 21.8 136.9 48.7 313.5 0.717 0.34 DIPA
(C.sub.6H.sub.15N) 19.1 234.4 83.5 79.4 0.717 0.40 DPA
(C.sub.6H.sub.15N) 22.3 227.7 109.3 24.1 0.738 0.50 TPA
(C.sub.9H.sub.21N) 22.4 178.4 158.0 1.5 0.753 .sigma..sub.L:
Surface Tension at 25.degree. C.; MV: Molecular Volume; BP: Boiling
Point; VP: Vapor Pressure at 25.degree. C.; .rho.: Density at
25.degree. C. (g/cm.sup.3); and .mu.: Viscosity at 25.degree. C.
(cp).
* * * * *